Two-cylinder pump for heavy flowable materials, such as concrete

ABSTRACT

A two-cylinder pump for heavy flowable materials, such as concrete, comprising a shutter mechanism which is pivotable across an apertured face plate, the shutter mechanism being sealed against the face plate by means of a cutting ring which is axially movable relatively to the shutter mechanism and is supported thereon with its rear side engaging a rectangular-section flexible rubber ring, whereby the cutting ring is urged resiliently against the face plate, means for locating the cutting ring, along a portion of its length, on the shutter mechanism, a seating for the flexible ring on the cutting ring which includes an annular extension which partly overlaps the longer cross-sectional side of the flexible ring in the axial direction, a seating for the flexible ring on the shutter mechanism which includes an annular extension which partly overlaps the longer cross-sectional side of the flexible ring in the axial direction, said annular extensions partly overlapping the ring from opposite sides thereof so that a part of the surface of the ring is left free between the annular extensions, and stops on the cutting ring and the shutter mechanism which limit the extent to which the cutting ring is inserted in said means for locating the cutting ring on the shutter mechanism.

BACKGROUND OF THE INVENTION

This invention relates to a two-cylinder pump for heavy flowablematerials, such as concrete, the pump having a shutter mechanism whichis pivotable across an apertured face plate, the shutter mechanism beingsealed against the face plate by means of a cutting ring which isaxially movable relatively to the shutter mechanism and is supportedthereon with its rear side engaging a rectangular-section flexiblerubber ring, whereby the cutting ring is urged resiliently aginst theface plate.

Such pumps must handle material which to a relatively large extentusually consists of hard particles of varying sizes, which in concretecomprise grains of sand and grit. In operation the shutter mechanismcarries out periodic movements in rhythm with the piston strokes in thecylinders, so as to connect the output cylinder with a delivery conduitand the input cylinder with a storage container. The cutting ringprovides a seal against the face plate, and also breaks up solidparticles which are present in the material and which get in the way ofparts moving in relation to each other when the shutter mechanism moves.Therefore the cutting ring must be urged against the face plate withconsiderable pressure. On the other hand, it must be able to moverelatively to the face plate and the shutter mechanism to compensate forwear of itself and the face plate.

It is known that the cutting ring can be prestressed mechanically by theshutter mechanism (German Offenlegungsschrift No. 23 62 670). For thispurpose the shutter mechanism, in the form of a swinging pipe, isresiliently connected by means of a swivel arm to a control shaft whichis axially movable for prestressing the swivel arm. However, this hasthe disadvantage that flexible distortion of the mechanical partsproduces a gap adjacent the face plate, and compensation for largeamounts of wear of the face plate and the cutting ring is not possible.

It is further known that this mechanical prestressing can be replaced byhydraulic prestressing (German Offenlegungsschrift No. 28 35 590), whichis variable in such a way that a greater contact pressure is producedwhen the shutter mechanism, in the form of a swinging pipe, is alignedwith one of the cylinder openings. From beginning to end of the swingingmotion, on the other hand, there is little contact pressure. Thisresults in the formation of a gap, which is dangerous due to the hardparticles in the material being transported. Moreover, prestressing byoil pressure is questionable on account of possible contamination of theconcrete by the hydraulic liquid.

In a further improved solution (German Offenlegungsschrift No. 26 32816), the cutting ring is prestressed without stressing the shuttermechanism, which is in the form of a swing pipe connected to theabove-mentioned swivel arm, in that the cutting ring is connected to ajoint on the swivel arm. However, by this means large amounts of wear onthe cutting ring and on the face plate cannot be compensated for in alldirections, so that sooner or later it will no longer be possible toprevent the formation of a gap.

It is known from German Offenlegungsschrift No. 29 03 749 that, by meansof the hydrostatic force of the material being transported, the shuttermechanism, which is in the form of an S-shaped swing pipe, can bepressed resiliently against the face plate hydrostatically and by theaxial compression of a rectangular section sealing ring clamped on thedelivery conduit. However, the mechanical compression of the flexiblerubber ring only produces low axial forces, since the seatings allow theflexible rubber ring to deflect inwardly along the whole axial length ofits inner surface. In this device the cutting ring is supported on abearing in which spherical surface interact with each other in order togive the cutting ring freedom of movement, which allows compensation forwear on the face plate and cutting ring.

The arrangement of the sealing ring, the swing pipe and its S-shape alllead to difficulties in carrying out the desired operations.

The viscosity of the material being transported in this type of swingpipe causes a drop in pressure to a specific degree. Also, in operatingthe pump the pressure drop can suddenly increase considerably, forexample if the shutter mechanism becomes clogged up. In this case, thecutting ring is only prestressed resiliently and therefore with much toolow a force. The gimbal bearings of the cutting ring for their partpresent considerable difficulties.

This invention therefore proceeds from a previously known solution(German Offenlegungsschrift No. 26 14 895). This is based on the conceptof, on the one hand, achieving the hydrostatic differential pressure,which presses the cutting ring with increased force on to the faceplate, by means of a lesser stressing of the sealing surface of thecutting ring by the hydrostatic pressure of the flowable material infavour of a greater stressing of the rear side of the cutting ring withthis pressure and, on the other hand, of prestressing the sealing ringnecessary for sealing the cutting ring radially, which sealing ring canalso be rectangular in cross-section, in such a way that the sealingring can for its part easily resiliently prestress the cutting ring.However, when in operation, this radial prestressing is not convertableinto any significant prestressing of the cutting ring on to the faceplate. Since the pump must work not only in a compression operation butalso in a suction operation, however, the sealing ring is often liftedfrom its seating during the suction operation of the pump and gets lostin the flowable material.

Moreover, there is also the disadvantage that the flexible rubbersealing ring and the cutting ring are only prestressed by the hydraulicpressure, since during the swinging movement of the shutter mechanisminsufficient pressure of the cutting ring on to the face plate isachieved. Compensation for wear is only possible by retightening theswing pipe bearing by means of several tie rods. However, this can incurconsiderable risks to the pump, since even a slight deviation of theswivel axis from its predetermined position can lead to significantdamage and destruction of the shutter mechanism. Large amounts of wearcannot be compensated for on the cutting ring, so that the formation ofa gap is automatically caused by wear. Moreover, with metallic expandingdevices which are used with a sealing ring consisting of an elastomer,it is not possible in practice to prevent this ring being lifted fromits seating.

The object of the present invention is, with a pump of thelatter-mentioned type, to achieve a reliable compression of the cuttingring on the face plate even during operation of the shutter mechanism,and automatic compensation for wear of the face plate and cutting ring,without any fear of losing the flexible rubber ring.

SUMMARY OF THE INVENTION

According to the invention there is provided a two-cylinder pump forheavy flowable materials, such as concrete, comprising a shuttermechanism, which is pivotable across an apertured face plate, theshutter mechanism being sealed against the face plate by means of acutting ring which is axially movable relatively to the shuttermechanism and is supported thereon with its rear side engaging arectangular-section flexible rubber ring, whereby the cutting ring isurged resiliently against the face plate, means for locating the cuttingring, along a portion of its length, on the shutter mechanism, a seatingfor the flexible ring on the cutting ring which includes an annularextension which partly overlaps the longer cross-sectional side of theflexible ring in the axial direction, a seating for the flexible ring onthe shutter mechanism which includes an annular extension which partlyoverlaps the longer cross-sectional side of the flexible ring in theaxial direction, said annular extensions partly overlapping the ringfrom opposite sides thereof so that a part of the surface of the ring isleft free between the annular extensions, and stops on the cutting ringand the shutter mechanism which limit the extent to which the cuttingring is inserted in said means for locating the cutting ring on theshutter mechanism.

It is hereby achieved that a long-stroke spring can be embodied with theflexible rubber ring. As is well known, this ring forms a Poisson's bodywhich does not change its volume on compression. Thus, on the one hand,according to this invention, the axial movement of the cutting ringlimited by the stops is selected so that, on maximum insertion of thecutting ring into its locating means, the flexible rubber ring cannot besqueezed out and lifted from its seating and, for example, carried alongby the material being transported. On the other hand, the free surfaceof the flexible rubber ring between the two annular extensions can beadjusted to the dimensions of the seatings in such a way that this ringcannot give way under pressure and the desired contact pressure can beachieved. By this means, the rear length of the cutting ring which isinserted into the locating means when in operation can be made so shortthat the cutting ring can be adjusted axially when wear takes place, andit can tilt during its pivotal movement if there is a large amount ofwear, and can thus compensate for this.

With a long-stroke flexible rubber annular spring of this type, the freesurface of the annular spring between the seatings can be deprived ofthe hydrostatic pressure of the material being transported, but themechanical prestressing of the annular spring can nevertheless be usedfor pressing the cutting ring on to the face plate. They can be combinedwith hydrostatic compression of the cutting ring by means of hydrostaticforces on differential surfaces on the cutting ring.

In other cases, the flexible rubber ring and therefore also its seatingson the cutting ring are exposed to the hydrostatic pressure .[.fo.]..Iadd.of .Iaddend.the material being transported, and it is mechanicallyprestressed in such a way that the cutting ring is pressed .[.on to.]..Iadd.onto .Iaddend.the face plate. These embodiments can also becombined with a hydrostatic prestressing of the cutting ring by means ofdifferential surfaces.

In general, one can proceed from the fact that, taken from the frontface of the cutting ring on the face plate side, the pressure is notconstant but is distributed depending on a function according to whichthe pressure decreases from the inside outwards. Since the opposite faceof the cutting ring and, inasmuch as the seating of the flexible rubberring is placed inside, also the seating of the cutting ring arecompletely loaded with the hydrostatic pressure, the hydrostaticcompression of the cutting ring over differential surfaces can generallybe achieved with a cylindrical inner surface of the cutting ring.However, the extent of this hydrostatic compression can be varied untilthere is a complete compensation of the differential forces existing onthe ring surfaces of the cutting ring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, so as to represent the motion cycle of the shutter mechanism,shows a diagrammatic view of the openings of the delivery cylinders of atwo-cylinder piston pump according to the invention, as a section alongthe line .[.B--B.]. .Iadd.I--I in FIG. 2,

FIG. 2 is a section along the line .[.A--A.]. .Iadd.II--IX to II--IX.Iaddend.in FIG. 1,

FIG. 3, in the illustration corresponding to FIG. 2, shows thisembodiment in simplified form, and below that shows a diagram of thestatic pressures which act directly on the cutting ring.

FIGS. 4 to 7 show modified embodiments of the invention in diagramscorresponding to FIG. 3,

FIG. 8 shows a further modified embodiment, and

FIG. 9 shows a particular operating condition of this embodiment, in adiagram corresponding to those of FIGS. 3 to 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The inner edges of the openings on the pipework side of the two deliverycylinders of a two-cylinder pump for heavy materials are indicated at 1and 2 in FIG. 1. A shutter mechanism 3 (FIG. 2) which is not shown indetail pivots through an arc 4 around a swivel axis 5. In its limitingpositions, shown by the dotted lines 6 and 7, the pivoting mechanism 3connects one delivery cylinder with the delivery conduit, which is notshown, whilst the other delivery cylinder is connected to an inputcontainer, from which it can draw in concrete. Therefore the pressure onthe shutter mechanism briefly subsides during the feed motion, if theflowable material can give way in the input container.

According to FIG. 2, a housing 8 in which the openings from the deliverycylinders are formed is covered with a face plate 9: this has apertures10 for each delivery cylinder which are aligned with the correspondingopenings 11 in the housing 8. The face plate 9 is attached to thehousing 8 by means of screws 12 with flush heads 13.

According to the embodiments shown, a cutting ring 14 provides theconnection with the shutter mechanism 3. As a modification of theembodiments, the cutting ring 14 could be placed in an intermediatering. It rests in a guide which is given the general reference numeral15, which is formed at the cylinder end 16 of the shutter mechanism 3.The guide consists of a cylindrical surface 17 at the end 16 of theshutter mechanism 3 and a corresponding cylindrical surface 18 on thecutting ring 14. In operation, the cutting ring 14 usually has a lengtha thereof inserted into the guide 15. Stop faces 19, 20 on the frontface of the end 16 of the shutter mechanism 3 or on an outer annularflange 21 of the cutting ring 14 serve as stops, which limit the lengthof the cutting ring inserted into the guide 15.

The embodiment of the invention illustrated in FIGS. 1 and 2 is shown inFIG. 3, but with only the parts which are important to the operationbeing shown. In the limiting positions of the shutter mechanism 3, thecutting ring 14 surrounds an opening 1 or 2. If, during operation of thepump the swinging movement of the shutter mechanism is carried out, thenthe material being transported which is wedged between the cutting ringand the face plate must be cut through, shortly before the limitingpositions are reached. In order to obtain full support of the cuttingring 14 during the cutting movements which occur between the cuttingring and the face plate, the ring is only directly supported along theshort length given the reference a, and for the rest is supported on aflexible rubber annular spring 23. The initial cross-section of theannular spring is that of a rectangle. It is arranged in such a way thatits shorter rectangular sides 24 and 25 extend radially, whilst thelonger rectangular sides 26 and 27 extend axially. When the annularspring is assembled with the device it is axially prestressed bymechanical means. Thereby the annular spring shapes itself in a curvealong its face lying between the seatings.

The seating of the annular spring 23 consists on the one hand of acylindrical extension 29 of the guide surface 17, which accordinglyextends axially, and also of radial surfaces 30 and 31, which in theembodiment shown are formed by rebates in the shutter mechanism 3 andcutting ring 14 respectively. Thereby, in all the embodiments shown, ascan be seen in the example in FIG. 4, annular flanges 33, 34 are formedon the shutter mechanism 3 and on the cutting ring 14, which partiallyoverlap faces 35, 36 of the flexible rubber annular spring 23. In theembodiment according to FIG. 3, the face 28 between the two annularflanges 33 and 34 remains free and is accordingly loaded with thehydrostatic pressure. During the delivery stroke of the pump, thecutting ring 14 is therefore pressed on to the face plate 9, both by themechanical prestressing of the annular spring 23 and also by the annularspring which bears on the cutting ring being loaded with the hydrostaticpressure of the material being transported. The mean diameter Dz (FIG.4) is determined by the guide 15. The radially inner limit of thecontact surface of the cutting ring 14 on the face plate is indicated bythe diameter Di, whilst the outer limit of this contact surface has thediameter Da. One can work on the following principle with sufficientaccuracy: as long as the mean diameter is closer to the outer diameterof the contact surface, there is an excess of hydrostatic pressure inthe direction of compression of the cutting ring on the face plate. Ifthe mean diameter bisects this contact surface, there is a pressureequilibrium. If it is smaller, then there is a hydrostatic differentialpressure which attempts to lift the cutting ring from the face plate. Bythis means one can allow the pressure produced by the prestressing ofthe annular spring to act alone, without hydrostatically supplementingit.

When sufficient clearance is allowed, as is indicated at 32 in FIG. 3,on the occurence of wear on the face plate or on the sealing surface 37of the cutting ring 14 facing the face plate, the cutting ring can tilt,and therefore total surface contact is guaranteed both in the newsituation and in the situation where there is wear.

The hydrostatic forces are shown in the lower diagram in FIG. 3. Herethe cutting ring 14 has a cylindrical inner surface 38. Whilst the rearside of the cutting ring, which is given the general reference numeral39 and which is loaded with the hydrostatic pressure up to the surface29, is loaded radially and uniformly with the hydrostatic pressure, thehydrostatic pressure decreases from the inside outwards, as is shown bythe curve 40 on the front face 41. The resulting forces are shown byarrows at 42 and 43; it can be seen that the hydrostatic forces whichload the cutting ring 14 in the direction of the face plate 9 aregreater than the forces 43.

In the embodiment according to FIG. 4, the force 45, acting upon thecutting ring 14 by lifting it up via a conical recess 44 on the frontface 41 of the cutting ring 14, is about as great as the force 46.However, forces 47 and 49 also act upon the cutting ring 14, which areessentially balanced. Nevertheless, by prestressing the annular spring23 a satisfactory sealing and a particularly small amount of wear isachieved with most materials.

According to FIG. 5, the prestressing forces of the cutting ring 14 liesomewhere between those in FIGS. 3 and 4. The forces 50 and 51 arebalanced. Forces 52 and 53 are not of equal size. The force 52 pressesthe cutting ring 14 hydrostatically against the face plate.Simultaneously, the briefly guided cutting ring 14 is hydrostaticallyloaded by means of the deformed annular spring 23 and is mechanicallyprestressed. A support ring 54 improves the mechanical properties of theflexible rubber ring and permits a greater clearance, which is shown at56. In this way, the load on the shutter mechanism 3 is transferred tothe cutting ring without any metallic contact.

According to the diagram in FIG. 6, by means of the surfaces 17 and 18the cutting ring guide is not in the axial position as in FIG. 2, butlies axially behind the annular spring 23, whereby the stop faces 19 areon the front face of the cutting ring 14, whilst the annular flange 21lies on the outer side of the shutter mechanism 3. Therefore, incontrast to the embodiment according to FIGS. 1 to 3, the oppositesurface 30 lies on the shutter mechanism 3.

The hydrostatic contact pressures 59 and 60 are unbalanced, so that thehydrostatic contact pressure 59 acting in the direction of the faceplate 9 is greater than the pressure 60 acting alone.

In the embodiment according to FIG. 7, the axial seating 31 of theflexible rubber annular spring 23 in the cutting ring 14, which has thegeneral formation shown in the embodiment according to FIG. 6, isdisplaced radially outwards, as opposed to its corresponding seating 30in the shutter mechanism 3. The hydrostatic contact pressures 61, 62 aretherefore equal. Therefore in this embodiment the cutting ring 14 iscompressed mechanically by the annular spring 23 and not hydrostaticallyon to the face plate 9.

In the embodiment according to FIG. 8, the annular spring 23 is notsubjected to the hydrostatic pressure of the flowable material, but inall operating conditions mechanically prestressed. The guide 15 of theshutter mechanism 3 and its annular extension 34 are therefore arrangedon the outer side. The front face 63 of the shutter mechanism 3 and theannular surface 64, which is loaded with the hydrostatic pressure forprestressing the cutting ring on to the face plate 9, serve as stopfaces for limiting the movement of the cutting ring, whereby the surface65 is also loaded with the hydraulic pressure, as can be seen from thediagram in FIG. 8. In this case the flexible rubber annular spring 23loses its sealing function, which in the embodiment according to FIG. 8is carried out by an O-ring 66, which is formed in a correspondinggroove 67 in the guide surface 17 of the cutting ring 14.

In the embodiment according to FIG. 8, the annular surfaces of thecontrol mechanism 3 and of the cutting ring 14, which are loaded withthe hydrostatic pressure, are formed in such a way that the axial forceson the ring 68 and 69 which are opposed to each other are unequal. Theforce 68 which is pressing down is greater than the uplifting force 69.

In the embodiment of FIG. 8 the stop faces 63 and 64 can abut oneanother, as shown in FIG. 9. This can occur, for example, during suddenwithdrawal, that is, lifting of the cutting ring 14 from the face plate9, perhaps if too hard particles have been cut through and the annularspring 23 has been compressed above its design limits. However, thissituation only occurs very occasionally.

The flexible rubber ring 23 generally consists of a plastics material,if one disregards the .[.prop.]. .Iadd.support .Iaddend.ring 54 which isprovided if necessary. In particular, natural rubber with soft flexibleproperties can be considered, but also butadiene mixture polymerides, orperhaps a butadiene vinyl pyridine polymeride.

With annular springs of this type, the cutting ring can behydrostatically pressed on to the face plate exclusively during thecontrol phase and, if necessary, additionally after build-up of thehydrostatic pressure.

I claim:
 1. A two-cylinder pump for heavy flowable materials, such asconcrete, comprising a shutter mechanism which is pivotable across anapertured face plate, the shutter mechanism being sealed against theface plate by means of a cutting ring which has a contact surface on itsfront end for contacting the face plate and which is axially movablerelatively to the shutter mechanism and is supported thereon with itsrear end engaging .[.a rectangular cross-section flexible rubber ring,the flexible ring.]. .Iadd.spring means .Iaddend.having first and secondsides which are aligned generally axially and first and second endswhich are aligned generally radially.[.,.]. .Iadd.with .Iaddend.thefirst and second sides being of greater length than the first and secondends.[., whereby.]. .Iadd.for urging .Iaddend.the cutting ring .[.isurged.]. resiliently against the face plate, means for locating thecutting ring, along a portion of its length, on the shutter mechanism,one of the shutter mechanism and the cutting ring having a supportsurface for engaging the first side of the .[.flexible ring.]..Iadd.spring means .Iaddend.along essentially its entire length, a firstseating for the first end of the .[.flexible ring.]. .Iadd.spring means.Iaddend.on the cutting ring which includes an annular extension whichpartly overlaps the second side of the .[.flexible ring.]. .Iadd.springmeans .Iaddend.in the axial direction, a second seating for the secondend of the .[.flexible ring.]. .Iadd.spring means .Iaddend.on theshutter mechanism which includes an annular extension which partlyoverlaps the second side of the .[.flexible ring.]. .Iadd.spring means.Iaddend.in the axial direction, said annular extensions partlyoverlapping the second side of the .[.flexible ring.]. .Iadd.springmeans .Iaddend.from opposite ends thereof so that a part of the secondside surface of the .[.flexible ring.]. .Iadd.spring means .Iaddend.isleft free between the annular extensions, and stops on the cutting ringand the shutter mechanism which limit the extent to which the cuttingring is inserted in said means for locating the cutting ring of theshutter mechanism.
 2. A pump according to claim 1, wherein the means forlocating the cutting ring on the shutter mechanism and the annularextension on the shutter mechanism are arranged on the outer side of theshutter mechanism and the shutter mechanism and cutting ring areprovided with annular faces which are subjected to hydrostatic pressurefor urging the cutting ring on to the face plate and which also serve asstop faces.
 3. A pump according to claim 1, wherein the means forlocating the cutting ring on the shutter mechanism is arranged on aninner side of the shutter mechanism, the free part of the second sidesurface of the .[.flexible ring.]. .Iadd.spring means .Iaddend.issubjected to the hydrostatic pressure of the flowable material, and thestops are provided by facing radial surfaces of the cutting ring andshutter mechanism respectively.
 4. A pump according to claim 1, whereinthe cutting ring has a cylindrical inner surface.
 5. A pump according toclaim 1, wherein the cutting ring has a conical inner surface, divergingtowards the face plate, which is subjected to the hydrostatic pressureof the flowable material.
 6. A pump according to claim 1, wherein theseating for the .[.flexible rubber ring.]. .Iadd.spring means.Iaddend.on the cutting ring is disposed opposite and radially outwardlyof the seating on the shutter mechanism.
 7. A pump according to claim 1,wherein the means for locating the cutting ring on the shutter mechanismincludes a cylindrical outer surface of the cutting ring and acylindrical inner surface of the shutter mechanism which engages theouter cylindrical surface of the cutting ring.
 8. A pump according toclaim 7, wherein the shutter mechanism includes an annular flange whichextends forward from the shutter mechanism toward the face plate,wherein the cylindrical inner surface of the support mechanism forms aportion of an inner surface of the annular flange, and wherein thesupport surface for engaging the first side of the .[.flexible ring.]..Iadd.spring means .Iaddend.along essentially its entire length forms aportion of the inner surface of the annular flange.
 9. A pump accordingto claim 8, wherein the stop on the shutter mechanism is a radialsurface at a forward end of the annular flange, and wherein the stop onthe cutting ring is a radial stop surface which extends outward from theouter cylindrical surface of the cutting ring.
 10. A pump according toclaim 8, wherein the first seating for the first end of the flexiblering.]. .Iadd.spring means .Iaddend.is defined by an outer surface ofthe annular extension of the cutting ring, a radial shoulder surface ofthe cutting ring which engages the first end surface of the .[.flexiblering.]. .Iadd.spring means.Iaddend., and the inner surface of theannular flange of the shutter mechanism.[.;.]..Iadd., .Iaddend.andwherein the second seating is defined by an outer surface of the annularextension of the shutter mechanism, the inner surface of the annularflange of the shutter mechanism, and a radial shoulder surface whichengages the second end surface of the .[.flexible ring.]. .Iadd.springmeans.Iaddend..
 11. A two-cylinder pump for heavy flowable materials,such as concrete, comprising a shutter mechanism which is pivotableacross an apertured face plate, the shutter mechanism being sealedagainst the face plate by means of a cutting ring which is axiallymovable relatively to the shutter mechanism and is supported thereonwith its rear side engaging .[.a rectangular cross-section flexiblerubber ring which has first and second sides and first and second ends,the side being of greater length than the ends whereby the cutting ringis urged.]. .Iadd.spring means having first and second sides which arealigned generally axially and first and second ends which are alignedgenerally radially with the sides being of greater length than the endsfor urging the cutting ring .Iaddend.resiliently against the face plate;a first cylindrical surface associated with the cutting ring and asecond cylindrical surface associated with the shutter mechanism forlocating the cutting ring, along a portion of its length, on the shuttermechanism; a support surface for engaging the first side of the.[.flexible ring.]. .Iadd.spring means.Iaddend.; a first seating for thefirst end of the .[.flexible ring.]. .Iadd.spring means .Iaddend.on thecutting ring which includes an annular extension which partly overlapsthe second side of the .[.flexible ring.]. .Iadd.spring means.Iaddend.in the axial direction, a second seating for the second end ofthe .[.flexible ring.]. .Iadd.spring means .Iaddend.on the shuttermechanism which includes an annular extension which partly overlaps thesecond side of the .[.flexible ring.]. .Iadd.spring means .Iaddend.inthe axial direction, said annular extensions partly overlapping thesecond side of the .[.flexible ring.]. .Iadd.spring means .Iaddend.fromopposite ends thereof so that a part of the second side surface of the.[.flexible ring.]. .Iadd.spring means .Iaddend.is left free between theannular extensions, and stops on the cutting ring and the shuttermechanism which limit the extent of axial movement of the cutting ringin a direction away from the face plate.
 12. A pump according to claim11, wherein the first cylindrical surface is a cylindrical outer surfaceof the cutting ring and the second cylindrical surface is a cylindricalinner surface which engages the outer cylindrical surface of the cuttingring.
 13. A pump according to claim 12, wherein the shutter mechanismincludes an annular flange which extends forward from the shuttermechanism toward the face plate, wherein the cylindrical inner surfaceforms a portion of an inner surface of the annular flange, and whereinthe support surface for engaging the first side of the .[.flexiblering.]. .Iadd.spring means .Iaddend.forms a portion of the inner surfaceof the annular flange.
 14. A pump according to claim 13, wherein thestop on the shutter mechanism is a radial surface at a forward end ofthe annular flange, and wherein the stop on the cutting ring is a radialstop surface which extends outward from the outer cylindrical surface ofthe cutting ring.
 15. A pump according to claim 13, wherein the firstseating for the first end of the .[.flexible ring.]. .Iadd.spring means.Iaddend.is defined by an outer surface of the annular extension of thecutting ring, a radial shoulder surface of the cutting ring whichengages .Iadd.a radial end surface of .Iaddend.the first end.[.surface.]. of the .[.flexible ring.]. .Iadd.spring means.Iaddend.,and the inner surface of the annular flange of the shutter mechanism,and wherein the second seating is defined by an outer surface of theannular extension of the shutter mechanism, the inner surface of theannular flange of the shutter mechanism, and a radial shoulder.[.which.]. surface .Iadd.which .Iaddend.engages .Iadd.a radial endsurface of .Iaddend.the second end .[.surface.]. of the .[.flexiblering.]. .Iadd.spring means.Iaddend..
 16. A two-cylinder pump for heavyflowable materials, such as concrete, the pump comprising:an aperturedface plate; a shutter mechanism which is pivotable across the aperturedface plate, the shutter mechanism having a forward end spaced from andfacing the face plate, a first annular flange which extends from theforward end axially toward the face plate, a second annular flange whichextends .[.radially.]. .Iadd.axially .Iaddend.from the forward endtoward the face plate and which is generally parallel to the firstannular flange, a generally radial shoulder surface between the firstand second annular flanges, the first and second annular flanges and theradial shoulder surface defining an annular groove, a generally axialsupport surface associated with the first annular flange, and agenerally radial stop surface; a cutting ring having a contact surfaceat a front end for contacting the face plate, a generally radialshoulder surface and an annular flange at a rear end, and a generallyradial stop surface for engaging the stop surface of the shuttermechanism to limit axial movement of the cutting ring with respect tothe shutter mechanism in an axial direction away from the face plate;.[.a long stroke spring in the form of a flexible ring having arectangular cross-section.]. .Iadd.spring means .Iaddend.with first andsecond sides which are aligned generally axially and first and secondends which are aligned generally radially.[., the flexible ring being.].positioned between the shutter mechanism and the cutting ring for urgingthe contact surface of the cutting ring resiliently against the faceplate, the first side of the .[.flexible ring.]. .Iadd.spring means.Iaddend.engaging the support surface of the shutter mechanism alongessentially an entire length of the first side, the first end of the.[.flexible ring.]. .Iadd.spring means .Iaddend.being positioned in afirst seating defined by the support surface of the shutter mechanismand the shoulder surface and the annular flange of the cutting ring sothat the annular flange of the cutting ring partly overlaps the secondside of the .[.flexible ring.]. .Iadd.spring means .Iaddend.in the axialdirection, and the second end of the .[.flexible ring.]. .Iadd.springmeans .Iaddend.being positioned in a second seating formed by theannular groove in the shutter mechanism so that the second flange of theshutter mechanism partly overlaps the second side of the .[.flexiblering.]. .Iadd.spring means .Iaddend.in the axial direction, the annularflange of the cutting ring and the second annular flange of the shuttermechanism being spaced from one another in the axial direction so that apart of the second side of the .[.flexible ring.]. .Iadd.spring means.Iaddend.is left free between the annular flange of the cutting ring andthe second annular flange of the shutter mechanism.
 17. A pump accordingto claim 16, wherein the cutting ring has a cylindrical outer surface,and wherein the first annular flange of the shutter mechanism has acylindrical inner surface which engages the outer cylindrical surface ofthe cutting ring.
 18. A pump according to claim 17, wherein the supportsurface forms a part of the inner surface of the first annular flange.19. A pump according to claim 16, wherein the stop .Iadd.surface.Iaddend.on the shutter mechanism is a radial surface at a forward endof the first annular flange. .Iadd.
 20. The pump of claim 1 wherein thespring means is a rectangular cross-section flexible rubber ring..Iaddend. .Iadd.21. The pump of claim 11 wherein the spring means is arectangular cross-section flexible rubber ring. .Iaddend. .Iadd.22. Thepump of claim 16 wherein the spring means is a long stroke spring in theform of a flexible ring having a rectangular cross-section. .Iaddend..Iadd.23. A two cylinder pump for heavy materials which has an aperturedface plate, a shutter mechanism pivotable across the face plate, acutting ring for sealing the shutter mechanism against the face platewith the cutting ring having a contact surface on its front end forcontacting the face plate and being axially movable relative to theshutter mechanism, spring means for urging the contact surface of thecutting ring toward the face plate, first means for retaining one end ofthe spring means in operable engagement with the cutting ring, andsecond means for retaining an other end of the spring means in operableengagement with the shutter mechanism, characterized in that the springmeans has first and second sides which are aligned generally axially andfirst and second ends which are aligned generally radially with thesides being longer than the ends, the spring means being positionedbetween the shutter mechanism and the cutting ring with the first sideof the spring means engaging a generally axial support surface on theshutter mechanism along essentially an entire length of the first sideand the first end of the spring means first being positioned in a firstseating defined by the first retaining means which includes an annularextension which partly overlaps the second side of the spring means inthe axial direction, and the second end of the spring means beingpositioned in a second seating defined by the second retaining meanswhich includes an annular extension which partly overlaps the secondside of the spring means in the axial direction so that a part of thesecond side of the spring means is left free between the annularextensions of the first and second retaining means. .Iaddend. .Iadd.24.The pump of claim 23 wherein the cutting ring has a cylindrical innersurface. .Iaddend. .Iadd.25. The pump of claim 23 wherein the shuttermechanism includes an annular flange which extends forward from theshutter mechanism toward the face plate, and wherein the inner surfaceof the annular flange forms the support surface for engaging the firstside of the spring means. .Iaddend. .Iadd.26. The pump of claim 25wherein the cutting ring has a cylindrical outer surface, and whereinthe annular flange on the shutter mechanism includes a cylindrical innersurface which engages the cylindrical outer surface of the cutting ring..Iaddend. .Iadd.27. The pump of claim 25 wherein the first retainingmeans is defined by an outer surface of the annular extension of thecutting ring, a radial shoulder surface of the cutting ring whichengages a radial end surface of the first end of the spring means, andthe inner surface of the annular flange of the shutter mechanism, andwherein the second retaining means is defined by an outer surface of theannular extension of the shutter mechanism, the inner surface of theannular flange of the shutter mechanism, and a radial shoulder surfaceof the shutter mechanism which engages a radial end surface of thesecond end of the spring means. .Iaddend. .Iadd.28. The pump of claim 23wherein the shutter mechanism includes an annular flange which extendsforward from the shutter mechanism toward the face plate, wherein thestop on the shutter mechanism is a radial surface at a forward end ofthe annular flange of the shutter mechanism, wherein the cutting ringhas a cylindrical outer surface, and wherein the stop on the cuttingring is a radial stop surface which extends outward from the cylindricalouter surface of the cutting ring. .Iaddend. .Iadd.29. The pump of claim23 wherein the spring means is a generally rectangular cross-sectionflexible ring. .Iaddend. .Iadd.30. The pump of claim 23 wherein thecutting ring and shutter mechanism have opposed stops aligned forengagement to limit the extent of axial movement of the cutting ringwith respect to the shutter mechanism in a direction away from the faceplate. .Iaddend. .Iadd.1. A two cylinder pump for heavy materials whichhas an apertured face plate, a shutter mechanism pivotable across theface plate which has an annular flange having an inner cylindricalsurface thereon and a radial surface at a forward end of the annularflange, an annular cutting ring for sealing the shutter mechanismagainst the face plate with the cutting ring having a contact surface onits front end for contacting the face plate, an inner cylindricalsurface of generally the same diameter as each aperture in the faceplate, and being axially movable relative to the shutter mechanism,axially extending spring means for urging the contact surface of thecutting ring toward the face plate with the spring means having firstand second sides which are generally axially aligned and first andsecond ends which are generally radially aligned, first means forretaining one end of the spring means in operable engagement with thecutting ring, and second means for retaining an other end of the springmeans in operable engagement with the shutter mechanism, characterizedin that the cutting ring has an annular extension on a rear end thereofwhich bears an outer cylindrical surface thereon that partly overlaps aninner annular side of the spring means in the axial direction, a radialshoulder surface which engages a radial end surface of one end of thespring means, an outer cylindrical surface which engages the innercylindrical surface of the annular flange of the shutter mechanism, anda radial stop surface which extends outward from the outer cylindricalsurface of the cutting ring for engagement with the radial surface onthe annular flange of the shutter mechanism to limit the extent of axialmovement of the cutting ring with respect to the shutter mechanism in adirection away from the face plate. .Iaddend. .Iadd.32. A two cylinderpump for heavy materials which has an apertured face plate, a shuttermechanism pivotable across the face plate which has an annular flangehaving a radial surface at a forward end thereof, a cutting ring forsealing the shutter mechanism against the face plate with the cuttingring being axially movable relative to the shutter mechanism, springmeans for urging the cutting ring away from the shutter mechanism, firstmeans for retaining one end of the spring means in operable engagementwith the cutting ring, and second means for retaining an other end ofthe spring means in operable engagement with the shutter mechanism,characterized in that the cutting ring has a contact surface at a frontend thereof for contacting the face place, a generally radial shouldersurface and an annular extension at a rear end thereof, and a generallyradial stop surface for engagement with the radial surface of theannular flange of the shutter mechanism to limit axial movement of thecutting ring with respect to the shutter mechanism in an axial directionaway from the face plate, and the spring means has first and secondsides which are aligned generally axially and first and second endswhich are aligned generally radially with the sides being longer thanthe ends, the spring means being positioned between the shuttermechanism and the cutting ring with the first side of the spring meansengaging a generally axial support surface on the shutter mechanismalong essentially an entire length of the first side and the first endof the spring means first being positioned in a first seating defined bythe retaining means which includes the annular extension of the cuttingring which partly overlaps the second side of the spring means in theaxial direction, and the second end of the spring means being positionedin a second seating defined by the second retaining means which includesan annular extension which partly overlaps the second side of the springmeans in the axial direction so that a part of the second side of thespring means is left free between the annular extensions of the firstand second retaining means. .Iaddend.